Evaluation of ligand selectivity using reporter cell lines stably expressing estrogen receptor alpha or beta

Estrogens control transcriptional responses through binding to two different nuclear receptors, estrogen receptor alpha (ER alpha) and beta (ER beta). Since these two ER subtypes are thought to mediate different biological effects, there is intense interest in designing subtype-selective ER ligands. In this study, we evaluated the ER alpha and ER beta selectivity of 19 known estrogens and antiestrogens using reporter cell lines previously developed in our laboratory. The HELN-ER alpha and HELN-ER beta cells stably express full-length ER alpha and ER beta, respectively, and are derived from HELN cells (HeLa cells stably transfected with an ERE-driven luciferase plasmid). We report that 16 alpha-LE2, PPT and 3 beta,5 alpha-GSD have a high ER alpha-selective agonist potency while 8 beta-VE2, DPN, genistein and biochanin A show ER beta selectivity with 8 beta-VE2 being the most potent and selective ER beta agonist. We also tested ER antagonists and we showed that raloxifene and RU486 are ER alpha and ER beta-selective antiestrogens, respectively. In all cases, selectivity is due to differences in binding affinities as indicated by whole-cell ligand-binding assays. Very interestingly, we demonstrate that a combination of genistein and raloxifene produces a full-ER beta specific response. Together these results demonstrate the usefulness of our stably transfected cell lines to characterize ER ligands and indicate that treatments combining agonist/antagonist ligands produce full-ER beta selectivity. (c) 2006 Elsevier Inc. All rights reserved.